Developing device for image forming apparatus

Abstract

An image forming apparatus including a photoconductive drum, a charger which charges the photoconductive drum, an exposing device which irradiates light to the charged photoconductive drum for forming an electrostatic latent image on the photoconductive drum, a developing device which has two component developer which includes magnetic toner and magnetic carriers and a transfer charger to transfer the developed image to a sheet of paper. The bias voltages of the charger, the developing device and the transfer charger are applied from a common high voltage power source. A developing starting voltage of the developing device is higher than a residual voltage of the photoconductive drum.

What is claimed as new and desired to be secured by Letters Patent of the United States is: 
     
       1. An image forming apparatus for forming a toner image on a sheet of paper, comprising: image bearing means;   charging means for charging said image bearing means;   means for forming an electrostatic latent image on said image bearing means;   developing means for developing said electrostatic latent image on said image bearing means;   transferring means for transferring said developed image; and   means for applying a bias voltage to said charging means, said developing means and said transferring means,   wherein said developing means includes a two component developer comprising magnetic toner and magnetic carriers, and   wherein said developing means comprises means for bearing said two component developer, means for regulating the thickness of said two component developer on said bearing means and means for adhering said two component developer on said bearing means, wherein said developing starting voltage is controlled in response to a gap between said image bearing means and said bearing means, a gap between said bearing means and said regulating means, a ratio of the surface velocity of said bearing means to that of said image bearing means, and an adhering force of said adhering means.   
     
     
       2. An apparatus as claimed in claim 1, wherein a developing starting voltage of said developing means is higher than a residual voltage of said image bearing means. 
     
     
       3. An apparatus as claimed in claim 1, wherein said charging means comprising a scorotron charger which has a charging electrode and a grid. 
     
     
       4. An apparatus as claimed in claim 1, wherein said applying means comprises a constant voltage power source. 
     
     
       5. An image forming apparatus, comprising: an image bearing device;   a charger which charges said image bearing device;   an exposing device which irradiates light to said charged image bearing device for forming an electrostatic latent image on said image bearing device;   a developing device which has developer for developing said image bearing device by said developer; and   a transfer charger to transfer said developed image to a medium, wherein a developing starting voltage of said developing device is higher than a residual voltage of said image bearing device,   wherein said developer includes a two component developer comprising magnetic toner and magnetic carriers, and   wherein said developing device comprises a developing sleeve which faces said image bearing device and bears said two component developer, a doctor blade which controls the quantity of said developer on said developing sleeve and a plurality of magnets which are provided in said developing sleeve, wherein said developing starting voltage is controlled in response to a gap between said image bearing device and said developing sleeve, a gap between said developing sleeve and said doctor blade, a ratio of the surface velocity of said developing sleeve to that of said image bearing device, and a magnetic force of said magnets.   
     
     
       6. An apparatus as claimed in claim 5, further comprising: a power source which is connected to said charger, said developing device and said transfer charger to apply a high voltage to said charger, said developing device and said transfer charger.   
     
     
       7. An image forming apparatus, comprising: an image bearing means;   charging means for charging said image bearing means;   means for forming an electrostatic latent image on said image bearing means;   a developing means for developing said electrostatic latent image on said image bearing means, wherein a developing starting voltage of said developing means is higher than a residual voltage of said image bearing means; and   means for transferring said developed image to a recording medium,   wherein said developing means includes a two component developer comprising magnetic toner and magnetic carriers, and   wherein said developing means comprises means for bearing said two component developer, means for regulating the thickness of said two component developer on said bearing means and means for adhering said two component developer on said bearing means, wherein said developing starting voltage is controlled in response to a gap between said image bearing means and said bearing means, a gap between said bearing means and said regulating means, a ratio of the surface velocity of said bearing means to that of said image bearing means, and an adhering force of said adhering means.   
     
     
       8. An apparatus as claimed in claim 7, further comprising means for applying a bias voltage to said charging means, said developing means and said transferring means. 
     
     
       9. An image forming apparatus for forming a toner image on a sheet of paper, comprising: image bearing means;   charging means for charging said image bearing means;   means for forming an electrostatic latent image on said image bearing means;   developing means for developing said electrostatic latent image on said image bearing means;   transferring means for transferring said developed image; and   means for applying a bias voltage to said charging means, said developing means and said transferring means,   wherein said means for applying includes a resistor between a high voltage power source and said developing means, and a variable resistor connected in series with a constant voltage device, said variable resistor and said constant voltage device being connected to a ground and to a point between said resistor and said developing means.   
     
     
       10. An image forming apparatus, comprising: an image bearing device;   a charger which charges said image bearing device;   an exposing device which irradiates light to said charged image bearing device for forming an electrostatic latent image on said image bearing device;   a developing device which has developer for developing said image bearing device by said developer; and   a transfer charger to transfer said developed image to a medium, wherein a developing starting voltage of said developing device is higher than a residual voltage of said image bearing device.